Experiments wil be performed to study synaptic release in the squid giant synapse of the stellate ganglion. Four kinds of experiments will be conducted in an attempt to elucidate further the mechanisms by which voltage-dependent calcium entry triggers transmitter release from the presynaptic terminal. (1) In the first set a direct visualization of calcium entry will be attempted using intracellular aequorin, light emission will be visualized directly with a microchannel plate image intensifier unit coupled to a silicone intensified television tube (SIT) unit and a frame grabbing device. This technique will give us further understanding of the spatial distribution of calcium entry into the presynaptic terminal during presynaptic voltage steps of varying amplitude and duration. The spatial visualization will provide insight into the relationship between the "threshold" for synaptic release and the distribution of intracellular calcium. (2) The voltage-dependence of synaptic release will be studied using direct intracellular calcium injections as well as transmembrane calcium current. Transmitter will be evoked by the above methods from different holding potentials in an efffort to elucidate the effect of membrane potential on the release process independently of the effect of voltage on calcium conductance. (3) A similar set of experiments will then be performed relating to temperature. Both double voltage clamp and calcium current injection would be utilized to attempt to separate the synaptic delay related to calcium entry from that relating to the subsequent steps leading to transmitter release. (4) Finally, the effect of "synaptic blockers", calcium channel blockers and presynaptic neurotoxins on the direct release following intracellular calcium injections will be utilized to determine which substances act as calcium channel blockers in this preparation and which may have direct effect on the intracellular calcium - transmitter release coupling mechanisms. The latter would then be studied to better understand the calcium release phenomenon.